Let me tell you why there is a huge fucking problem with this right now.
Right now, when you plug in a ps3 stick/controller, it has to be assigned to an account. To sign in to an account you need a ps4 pad. Player two will ALSO need to sign into an account (Guest1, no psn).
Scenario 1: Player 1 PS4 Pad, Player 2 PS3 Stick, no pad.
Player Two will control Player One. There is no way to have player two join as player two.
Scenario 2: Player 1 PS4 Pad, Player 2 PS3 Stick, Ps4 Pad.
Player Two will have to Sign In under Guest 1. This is so that they can sign in as player two.
What does this mean? BRING A PS4 CONTROLLER WITH YOU TO AN EVENT.
What will we have to do after the match? DESYNC YOUR PS4 CONTROLLER VIA THE DESYNC STATION*
This is what we will have to do if this doesn't get fixed. If that's not the case and this causes too much of a clusterfuck, banning legacy controllers might be the right way.
*A Desync station is a PS4 system off to the side where you can plug in your PS4 pad to sync up with that station. This station will not be used for tournaments and will not have any issues taking in controllers.